1. Field of the Invention
This invention relates to a self-contained closed circuit breathing apparatus. More particularly, this invention relates to a self-contained closed circuit breathing apparatus which is able to control the distribution of respiratory work between exhalation and inhalation. Balancing this breathing work load in such closed circuit breathing apparatus proves a significant physiological advantage since it is well known that balanced resistance, i.e. balanced exhalation and inhalation pressure is tolerated much better by wearers of breathing apparatus than are breathing apparatus systems which have unbalanced resistance.
2. Description of the Prior Art
All commercially available closed circuit breathing apparatus approved under 30 CFR 11 and being used today do not have balanced inhalation and exhalation resistance. This is because all exhalation flow passes through a carbon dioxide-removing chemical canister at high resistance before entering the breathing bag. Upon inhalation, the gas passes out of the breathing bag into the mouthpiece at low resistances. Thus, in these apparatus exhalation resistance is much higher than inhalation resistance.
Resistance is directly related to flow rate through the apparatus [R=K (flow rate).sup.n ] where R is resistance, K is a constant, and n is a number between 1 and 2 depending on whether the flow rate is laminar or turbulent. Since resistance is directly related to the flow rate, a lower flow rate means a lower resistance. In a closed circuit breathing apparatus, the CO.sub.2 -removing canister has the highest resistance to the flow rate. Therefore, if the flow rate through the canister can be reduced during exhalation, then resistance to exhalation flow rate will be reduced.
U.S. Pat. No. 3,837,337 to Paul A. LaViolette describes a self-contained closed circuit breathing apparatus which embodies a dual air bag system. In accordance with the invention of U.S. Pat. No. 3,837,337, a positive pressure bag is positioned upstream of the carbon-dioxide removing canister and a negative pressure bag is positioned downstream of the canister. During the exhalation portion of the cycle, a positive pressure is built up in the positive pressure bag, whereas during the inhalation half of the cycle a negative pressure is created in the negative pressure bag. As the pressure in the two bags tends to equalize itself by flowing through the canister, flow can take place throughout the complete breathing cycle. This means that the dual bag system of the patent evenly distributes the respiratory work between inhalation and exhalation. One shortcoming of the dual bag system of the patent, however, is that it cannot be adjusted to other distribution patterns.
Moreover, it is necessary that the dual bags in the invention of U.S. Pat. No. 3,837,337 must either have a resilient means such as in elastic material construction or be subjected to spring forces. This can lead to increased weight and complexity as well as the potential problem of toxic gas permeation. In addition, if the bags are not resilient, the breathing resistance will be erratic with high peak pressures.
It is an object of the invention, therefore, to provide a self-contained closed circuit breathing apparatus which is capable of dividing the respiratory work between inhalation and exhalation in predetermined proportions.
Another object of the invention is to provide a self-contained closed circuit breathing apparatus which can provide a controlled range of proportionate respiratory loads between inhalation and exhalation without the necessity of resilient means such as elastic bags and spring forces.
Yet another object of the invention is to provide two small and variable sized breathing bags to increase variability in the design of closed circuit breathing apparatus.